The use of transformed eucaryotic hosts to express a desired foreign protein is known in the art through the use of recombinant DNA techniques. The transformed cells containing a vector having DNA coding for the desired foreign protein are then grown in cell culture using conventional techniques and the foreign protein, if secreted by the transformed host, is isolated from the cell culture fluids or, if not secreted, is isolated by rupturing the cells.
A modification of the fermentation techniques is to employ a vector which does not produce the desired foreign protein until a specific nutrient is added to the culture medium. Galactose is such a nutrient medium which can be used to induce expression of the desired foreign protein using techniques known to the art (Stepien et al., Gene 24: 289-298, 1983). While the galactose induction system works well to initiate expression of the desired foreign protein in batch mode, it works poorly in fed-batch mode. It would be desirable to obtain the desired protein in higher yield using fed-batch mode.